Variable expansion ratio nozzle



March 5, 1963 R. F. THIELMAN VARIABLE EXPANSION RATIO NOZZLE v. M/Z/Z/f i a l. I U

Filed Feb. 23, 1961 INVENTOR- Fuxe/Z F Tte/marz BY 7/21/72 4 A TTORN United States Patent 3,079,752 VLE EEQANSE N RATE) NOZZLE Russell F. Thielman, Cleveland, Ghio, assignmto Thompson Rama Wooldridge Inc, Cleveland, (lino, a corporation of Ohio Filed Feb. 23, 1961, Ser. No. 91,271 5 Claims. (Cl. oil-35.6)

This invention relates to air and space borne vehicles and is more particularly directed to improved methods and means for varying the gas expansion ratio of a gas discharge nozzle for reaction motors propelling such vehicles.

Heretofore, various attempts have been made to control and maintain the most ellicient thrust level of air and space borne vehicles, such as rockets, missiles, satellites, nose cones and the like, for example, by varying the throat area A, with a movable probe to provide a variable ratio nozzle assembly. Combustion chamber pressures, under some circumstances, are controlled as a function of the pressure in the exhaust exit portion of the nozzle for this purpose. All such attempts involved complicated equipment and added considerably to the weight of the vehicle. In addition these probe and pressure arrangements included moving parts which decreased the reliability of their use and thus the overall reliability of the missile or rocket with which employed.

' I substantially overcome the difiiculties and problems of the prior art with apparatus constructed in accordance with the principles of my invention wherein a plurality of concentric inner nozzle exit portions are removably secured to the outer nozzle exit portion which may be fixedly attached to the nozzle structure for sequential ejectment thereof from the nozzle to provide an overall nozzle assembly capable of providing variable gas expansion ratios.

' It therefore is an object of the present invention to provide improved gas discharge nozzle assemblies for reaction motors providing the thrust for air and space borne vehicles.

It is another object of the present invention to provide an improved gas discharge nozzle for reaction motors employing a plurality of concentric ejectable nozzle exit portions.

It is another object of the present invention to provide an improved nozzle assembly for reaction motors having one or more nozzle exit portions which are ejectable sequentially to vary the nozzle expansion ratios of the reaction motor.

It is a further object of the present invention to provide nozzle assemblies for reaction motors including at least one ejectable nozzle portion bonded to the primary nozzle exit portion of the nozzle assembly which is ejectable at a predetermined time.

Yet another object of the present inention is to provide improved methods for varying the expansion ratio of reaction motors.

These and other objects, features and advantages of the present invention will become more apparent from a careful consideration of the following detailed description when considered in conjunction with the accompanying drawing illustrating preferred embodiments of the present invention and wherein like reference numerals and characters refer to like and corresponding partsthroughout the several views.

On the-drawing:

FIGURE 1 is a view in longitudinal section of a nozzle assembly constructed in accordance with the principles of the present invention;

FIGURE 2 is a view in cross section taken along lines 11-11 of FIGURE 1;

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FIGURE 3 is a view in longitudinal section illustrating an alternative embodiment of the present invention;

FIGURE 4 is a view in cross section taken along lines IV-IV of FIGURE 3.

As shown on the drawings:

Briefly stated, the present invention involves forming a reaction nozzle having a nozzle exit portion sized to provide the maximum gas expansion ratio desired and an ejectable inner nozzle exit portion sized to provide the minimum gas expansion ratio desired.

It can be shown that the force or thrust of a reaction motor, obtained by summing up internal pressures in the reaction chamber, in the nozzle entrance portion; throat, and exit portion and the external pressure or atmospheric pressure, equals the force obtained by the momentum principle or:

where v equals rocket exhaust gas exhaust velocity, g is a conversion factor w is the weight flow rate or the propellannp the nozzle exit portion pressure, 17 atmospheric pressure or external pressure, and A the exhaust gas nozzle exit area. The pressure thrust term (p -11914 consists of the 'pres sure difierence between the nozzle exit pres-sure (p and atmospheric pressure (12 multiplied by the nozzle exit area A It will be appreciated that from this equation accurate values of thrust variation with altitude are obtainable. From the momentum principle, the ideal thrust equation F=C Atp A, is the cross-sectional area of the throat of the nozzle,

p, is the reaction chamber pressure and C, is the thrust coefficient of the ideal thrust equation.

The trust coefiicient C is defined as follows:

K equals the specific heat ratio, 17 the reaction chamber pressure, p the nozzle exit portion pressure, A the nozzle exit cross-sectional area, and p the external or atmospheric pressure and A throat cross-sectional area. 7

It will be appreciated that the thrust of the air or space borne vehicle is therefore a linear function of the thrust coefficient Cf. It will also be appreciated that the magnitude of the thrust coefiicient is fixed by a combustion pressure-atmospheric pressure ratio and the rocket nozzle expansion ratio. Thus, for a given combustion pressureatmospheric pressure ratio, there exists a maximum or optimum value of C Corresponding to this maximum value then there is one optimum nozzle expansion ratio. It will be appreciated therefore that in rocket nozzle dc sign, that structure which permits the expansion of the propellant products, i.e., the exhaust gases, to the pressure that is exactly equal to the pressure of the surrounding fluid, i.e., atmospheric pressure is referred to as the nozzle design with optimum expansion ratio.

ay be derived. Simplified, the ideal thrust equation 'ing of the reaction motor commences.

efiicient C; is at a maximum at a given nozzle expansion ratio for only one value of combustion pressure-atmospheric pressure, atmospheric pressure changes will cause a reduction in thrust since all the remaining design parameters of the reaction motor are fixed. This theory is ably discussed in the text entitled Rocket Propulsion Elements by George P. Sutton, copyright by John Wiley and Sons, Inc., Second Edition, New York.

' Although the present invention has a variety of applications, an embodiment thereof appearing in FIGURE 1 includes a reaction motor, generally indicated by them;- meral 6, defining a reaction chamber 7 having secured thereto as at 8 by pinsB a nozzle assembly, generally indicated by the numeral 19. Flow between the inner wall 7a of the reaction chamber and the outer wall 11 of the nozzle is prevented by an annular seal means 12 seated in a groove formed in either the nozzle or reaction chamber inner wall 711.

The nozzle assembly 10 is of the DeLaval type and includes -a nozzle'entrance portion 13, a nozzle throat 14 and a nozzle exit portion 15, The nozzle exit portion 15 may be a separate member fixedly secured to the nozzle throat portion or may be formed integrally therewith as appears in FIGURE 1. The nozzle exit portion 15 defines a divergent gas flow path for the exhaust gases emanating from the reaction chamber 7. The nozzle exit nozzles are bonded in accordance with the procedures and portion 15 is sized to provide the maximum gas expan- 'sion ratio of the reaction motor desired for a particular 7 programmed mission of the vehicle.

Removably secured to the inner wallof the nozzle exit wall 15 adjacent the throat 14 is an ejectable nozzle insert 16 sized to provide the lowest expansion ratio for the programmed mission of the vehicle propelled by the reaction motor. The inner surface 16a of the nozzle insert 16 is sized to the throat exit portion 14a to minimize discontinuities therebetween and thus prevent undesirable efiects on the primary flow of exhaust gases through the nozzle assembly 10. The outer surface 16b of the nozzle 7 exit insert 16 is bonded as at 18 to the wall 15a of the outer nozzle exit portion 15. V

The nozzle exit insert 16 may be bonded by a low temperature adhesive, such as a phenolic resin, and the wall thickness adjacent the bonding joint is preferably at thickness of the wall of the insert 16 are taken into consideration in determining the point at which the insert will be expelled from the nozzle.

At a high atmospheric pressure, a low nozzle expansion ratio is dictated to achieve the maximum thrust co- 'efiicient. Thus, a high exit portion pressure is required. At low atmospheric pressures, a considerably higher nozzle expansion ratio is required for lower atmospheric pressures and consequently low pressures at the exit of the nozzle exit portion.

In operation, the joining material 18 is designed to melt or evaporate at a specific time interval after the fir- When the joint material 18 meltsor is burned away, the nozzle exit portion insert 16 is blown out of the nozzle. The exhaust gases discharging through the nozzle now expand along the outer exit portion 15. Thus as the vehicle increases in altitude, the higher expansion ratio of the integral exit portion 15 of the nozzle maximizes the thrust coefiicient C, for the low atmospheric pressure of the next phase of flight; The inner expellable insert 16 is sized to prowith the materials outlined above. 7

In the operation of the apparatus of FIGURE 3, an

innermost insert 22 is bonded by a material 18 which will cause its ejectmen-t before the other nozzles inse1ts'21 and 2-9. Similarly, the bonding material for the nozzle insert 21 permits ejectment thereof. before the nozzle insert 2i).

It will be appreciated that the nozzle assemblies of the present invention are particularly suitable for employment with underwater vehicles or missiles launched from underwater since the ejectable nozzle exit portion inserts may be employed in sufiicient number to operate efiiciently over widely varying nozzle exit portion pressures.

Thus, it will be appreciated that with my invention 7 I provide improved means for varying the expansion ratio of the exit portion of a vehicle propelled by gases generated in a reaction motor. of the present invention permits sequential increase of the expansion ratio of the exit portion of the nozzle to compensate for decreases in atmospheric pressures.

7 Although various minor modifications of the present invention may be readily apparent to those versed in the art, it should be understood that I wish to embody within the scope of the patent warranted hereon all such em bodiments as reasonably and properly come within the scope of my contributionto the art.

I claim:

1. A variable expansion ratio gas discharge nozzle assembly adapted to discharge gases generated in the combustion chamber of a jet propulsion engine, or the like, comprising: a relatively fixed outer convergent-divergent nozzle adapted to be secured to said combustion chamher and sized to provide a maximum expansion ratio, a plurality'of releasable divergent portions, each of said divergent portions being arranged substantially entirelyv within the divergent section of said nozzle with the for-,

ward edge of eachdivergent portion abutting the divergent wall of said fixed nozzle, said portions being concentric and substantially axially aligned, the innermost portion providing a minimum expansion ratio, means for releasablysecuring said portions to the divergent wall of said .nozzle and adapted to sequentially release said portions means comprises a low temperature adhesive substance bonding each divergent portion to the nozzle wall.

3. The combination of claim 2 wherein the adhesive substance holding the innermost portion is adapted to melt at a specific time interval after firing of the engine and the adhesive substance on the next outer portion is adapted to melt at a specific longer time interval after firing.

4. A variable expansion ratio gas discharge nozzle assembly adapted to discharge gases generated in the combustion chamber of a jet propulsion engine, or the like, comprising: a relatively fixed outer convergent-divergent nozzle adapted to be secured to said combustion chamber and sized to provide a maximum expansion ratio, a releasable divergent portion, said divergent portion being Each of the V The nozzle assembly arranged substantially entirely within the divergent section of said nozzle with the forward edge of said divergent portion abutting the divergent wall of said fixed nozzle, said releasable divergent portion sized to provide a minimum gas expansion ratio, a low temperature adhesive substance bonding said releasable portion to the nozzle wall and adapted to be released in time delay response to a predetermined increase in the temperature of the nozzle assembly.

5. The combination of claim 4 wherein said adhesive substance is adapted to melt at a specific time interval after firing the engine.

References Cited in the file of this patent UNITED STATES PATENTS Skinner July 2, 1940 Bradford May 13, 1952 Welsh Oct. 16, 1956 Kappus Apr. 7, 1959 Whitrnore Nov. 17, 1959 Kimrnel Sept. 20, 1960 Davidson May 23, 1961 FOREIGN PATENTS Great Britain May 27, 1959 

1. A VARIABLE EXPANSION RATIO GAS DISCHARGE NOZZLE ASSEMBLY ADAPTED TO DISCHARGE GASES GENERATED IN THE COMBUSTION CHAMBER OF A JET PROPULSION ENGINE, OR THE LIKE, COMPRISING: A RELATIVELY FIXED OUTER CONVERGENT-DIVERGENT NOZZLE ADAPTED TO BE SECURED TO SAID COMBUSTION CHAMBER AND SIZED TO PROVIDE A MAXIMUM EXPANSION RATIO, A PLURALITY OF RELEASABLE DIVERGENT PORTIONS, EACH OF SAID DIVERGENT PORTIONS BEING ARRANGED SUBSTANTIALLY ENTIRELY WITHIN THE DIVERGENT SECTION OF SAID NOZZLE WITH THE FORWARD EDGE OF EACH DIVERGENT PORTION ABUTTING THE DIVERGENT WALL OF SAID FIXED NOZZLE, SAID PORTIONS BEING CONCENTRIC 